NOS electrolytic capacitor - Can I use them ???

[kagliostro]

With other material I got some (20-30) NOS electrolytic capacitors

they are very nice, those here in Italy we call "condensatore a vitone", due to the montage way

must consider to reform it before use ??

do you think I can use it safely ?

Kagliostro

[bigsbybender]

Many sit on shelves for years before use. How old are they?

It may be worth a try if you have many of them, but reform them and perhaps buy a capacitance meter before I risk using them in an amp.

[kagliostro]

I've a capacitance meter but absolutely don't know how many years they have

tomorrow I'll try to look if I find some clues printed on them

about reform it which voltage is better to use (start voltage / arrival voltage,  respect the rated voltage of the cap) ?

I've also read it will be better to put a limiting resistor in series to prevent demage of the power supply if the cap is bad

also, do you think is better (as I've read) to put it in hot water for some time, to help the electrolyte to return at his original conditions, before to reform it ?

Thanks

Kagliostro

[Willabe]

Try this;                http://www.electrojumble.org/reforming.htm

The author says it works,  --- if --- you reform them right.

It seems that a current limit is what keeps the cap that is being reformed from over heating, and that is the key. Too much leakage and the cap over heats and it's toast. So limiting the current lets the cap reform slowly. You start with about 1/4 the voltage raiting and wait untill the leakage current from the cap stablizes, then you up the voltage a little more and wait untill the leakage stablizes and then repeat untill you bring the cap up to full voltage. I've done this with a power supply on a variac and the cap stoped leaking after some time and seemed to become stable with little leakage current. It took an hour or two for this to happen. Now how long the cap will last after doing this..... I don't know.         Audio guys say it works. Can't hurt to try it.

GW talks about, in one of his books, of warming up the caps to "melt" the lytic paste, but said he never tried it. I think he said about 125f for an hour or so. Now he was talking about doing this by itself and not as a 1st step in reforming the cap. Maybe your on to something here. Maybe if the cap is warmed a little at first, that would shorten the time it takes to reform the cap?            

I think it's not only about bringing the capacitance value back but what about the ESR? I think you would have to be able to restore both.

If you try this let us know what you think/find.


        Brad        


                

[kagliostro]

Thanks

my hope is that if reforming give a new life to old used capacitors, with NOS capacitors the result is supposed to be better (I HOPE)

Kagliostro

[SoundmasterG]

I've got a Sprague Tel-ohmike (VERY useful) which can be used to reform caps. It can supply up to 600v and limits the current internally. I used it along with an external resistor to be sure and reformed some 15 year old LCR can caps that had never been used. They seem to work just fine, though I would never use them in an amp for sale or repair...only my own stuff.

Greg

[kagliostro]

Thanks

it is interesting to hear your experience about

Kagliostro

[tubeswell]

Simcha Delft explained this process to me once. IIRC you hook up a chunky resistor in series with the cap and connect it to a variac, then you put the variac on a low voltage and measure the voltage drop across the resistor until the voltage drop goes away, then you increase the variac voltage and repeat ad-nauseum, until you have the variac running at the desired voltage that you want the cap to operate at, then some. JM2CW

[kagliostro]

you hook up a chunky resistor in series with the cap and connect it to a variac, then you put the variac on a low voltage and measure the voltage drop across the resistor

Thanks Tubeswell

do not forget anything ? .............. something like a diode and/or a rectifier ..............

No, joke, of course it is understood

Kagliostro

[Willabe]

kagliostro,

Have you tried reforming any caps yet?

If so what do you think? Any results good or bad?


          Brad